title: On the role of calcium ions in the regulation of glycogenolysis in mouse brain cortical slices.
abstract: Using mouse brain cortical slices, we investigated the relative roles of cyclic AMP and of calcium ions as the intracellular messengers for the activation of glycogen phosphorylase (EC 2.4.1.1; alpha-1,4-glucan:orthophosphate glucosyltransferase) induced by noradrenaline and by depolarization. Activation of phosphorylase by 100 microM noradrenaline is mediated by beta-adrenergic receptors and does not require the copresence of adenosine. The role of the concomitant small increase in cyclic AMP is questioned. Short-term treatment with EGTA or LaCl3 abolishes the noradrenaline activation of phosphorylase, pointing to a critical role of extracellular calcium. Depolarization by 25 mM K+ or 100 microM veratridine produces a rapid and large (fourfold) activation of phosphorylase. Only veratridine increases the cyclic AMP levels; exogenous adenosine deaminase essentially blocks this cyclic AMP accumulation but not the phosphorylase activation. A half-maximal activation of phosphorylase occurs at about 12 mM K+. Addition of EGTA or LaCl3 reduces the effect of both depolarizations to a slight and transient activation of phosphorylase. These results indicate that activation of glycogen phosphorylase by K+ or veratridine occurs by a cyclic AMP-independent and calcium-dependent mechanism. The calcium dependency of brain phosphorylase kinase renders this kinase the prime target enzyme for regulation of glycogenolysis by calcium ions.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D006003:Glycogen / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D051379:Mice; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D006005:Phosphorylases / Q000378:metabolism
chemical_list: C028521:lanthanum chloride; D010656:Phenylephrine; D004533:Egtazic Acid; D007811:Lanthanum; D006003:Glycogen; D006005:Phosphorylases; D007545:Isoproterenol; D003000:Clonidine; D002118:Calcium; D009638:Norepinephrine; D004837:Epinephrine